Every single human consists of thousands of genes, billions of neurons and trillions of bacteria. There is a rapidly growing number of data that links the gut microbiome to the development and functioning of the central nervous system, which is a currently proposed paradigm shift in neuroscience. Knowledge on the relationship between gut microbiota and mental disorders is constantly increasing. This phenomenon is known as “gut-brain axis”. The strongest evidence for the role of microbes in the gut-brain axis comes from animal studies. Nevertheless, the gut-brain crosstalk is a bidirectional communication system that not only provides gastrointestinal homeostasis, but can also affect motivation as well as higher cognitive functions. Moreover, gut microbiome can be associated with obesity and inflammatory gastrointestinal disorders. According to the recent studies, there is a link between the composition of gut microbiota and mental disorders in animals (response to depression and chronic stress). This subject requires further examination, especially taking into consideration